In true full duplex communication, a device both sends and receives data simultaneously in the same channel and frequency band. Many older devices simulate full duplex communication using either frequency division multiplexing or time division multiplexing. As wireless technology evolves, more wireless devices support true full duplex communication.
FIGS. 1A and 1B illustrate the difference between half duplex and full duplex communication between two stations and an access point in a wireless local area network (WLAN). Station 1 and the access point are both full duplex capable, while station 2 is not full duplex capable. A full duplex capable device is a device that is operable to simultaneously send and receive data in the same channel and frequency band. As shown in FIG. 1A, in half duplex communication, after waiting a backoff period to ensure that no other devices are communicating in a channel, station 1 determines that it can grant itself a transmission opportunity (TXOP) which is a bounded time interval during which station 1 can send as many frames as possible to the access point. When the TXOP begins, station 1 sends a frame or frames containing “Data 1” to the access point. Station 1 determines how many frames it can send based on the duration of the TXOP. When the access point has successfully received the frames, the access point sends an acknowledgement frame (ACK) to station 1.
To send data to station 1 and station 2, after waiting a backoff period to ensure that no other devices are communicating in a channel, the access point determines that it can grant itself a TXOP. When the TXOP begins, the access point sends a frame or frames containing “Data 2” to station 1, receives an ACK frame from station 1 and then sends a frame or frames containing “Data 3” to station 2. When station 2 has successfully received the frames, station 2 sends an ACK to the access point. The access point determines how many frames it can send to station 1 and station 2 based on the duration of the TXOP.
FIG. 1 B illustrates how allowing station 1 and the access point to utilize their full duplex communication capability saves time and overhead. Although FIG. 1B and other figures may not show the PHY header, it is understood that when a frame is transmitted, the frame is always carried in a Physical Protocol Data Unit (PPDU) (e.g., the data portion of the PPDU) and follows the PHY header of the PPDU as shown in FIGS. 3 and 4. After waiting a backoff period to ensure that no other devices are communicating in a channel, station 1 determines that it can grant itself a TXOP. When the TXOP begins, station 1 sends a frame or frames containing “Data 1” to the access point. Station 1 determines how many frames it can send based on the duration of the TXOP. At the same time, the access point sends a frame or frames containing “Data 2” to station 1. The access point determines how many frames it can send based on the duration of the TXOP. When the access point has successfully received the frames, the access point sends an ACK to station 1. When station 1 has successfully received the frames, station 1 sends an ACK to the access point. Note how much time is saved (e.g., the time for the separate transmission of Data 2 to station 1) when full duplex mode is used instead of half duplex mode.